In World War II, there was a Spanish spy named Joan Pujol Garcia who approached the Allies to work for them. When they refused, he approached the Nazis, and they accepted him (giving him the codename Arabel). Once he earned credentials working as a Nazi spy, he approached the Allies again, this time getting a job as a double agent (codenamed Garbo).
He fed the Germans a combination of mis-information, true but useless information, and high-value information that always got to the Germans just a little too late. He even started a spy network consisting of 27 sub-agents of his own. Keep in mind that not a single one of these sub-agents existed. They were completely imaginary, but regardless, he submitted expense reports for them and had the Nazis giving him money to pay their salaries. At one point, when he had to explain why some high-value information got to the Germans late, he told them that one of his spies had died. He actually got the Germans to pay the imaginary spy’s imaginary wife a very real pension for her loss. Not only did his false information get the Nazis to waste millions of dollars, but he was also instrumental in convincing the Nazis that the attacks on D-Day were just a diversion, and the real attack was yet to come, keeping vital German resources away from the front lines.
He is one of the only people to ever get an Iron Cross from the Germans (which required Hitler’s personal authorization, since he wasn’t a soldier) AND an MBE from King George VI.